1. Field of the Invention
The present invention relates to networks, private branch exchanges (PBXs), wireless local-area-network (LAN) terminals, and multiprotocol communication-terminal control methods therefor, and, more particularly, to a terminal connected to a network including an internet-protocol (IP) private branch exchange.
2. Description of the Related Art
This type of network has heretofore been constituted by connection of a private branch exchange to a fixed phone terminal, a radio terminal such as a personal handy-phone system (PHS), a voice over Internet protocol (VoIP) terminal or the like via a local area network (LAN).
As the VoIP terminal, in addition to an IP phone terminal and an Internet phone terminal, there is a session initiation protocol terminal. The SIP is a communication protocol for use in starting or ending multimedia communication such as sound communication (fixed phone, cellular phone, etc.), video communication such as television phone, chat (conversation by characters) and the like in an environment of an IP network using data having a form referred to as an IP packet.
In the IP network, in general, connection-less type communication is performed without confirming connection to a target as in electronic mails. On the other hand, in the fixed phone, in general, connection type communication is performed while confirming the connection with the target. The SIP realizes the connection type communication in the IP network.
The SIP basically comprises methods (operations) such as INVITE (session between users is established), ACK (acknowledgment), CANCEL (INVITE is ended during the establishment of the session), and BYE (the end of the session). The respective methods are exchanged as requests and responses to the requests between clients and servers to thereby establish or end the session.
Moreover, the SIP has characteristics that applications can be comparatively easily prepared. For example, when a new service is added to H.323 of ITU-T for use in the IP phone, an H.450.x protocol which defines the H.323 additional service is added, and all H.323 end points on the network and software of a gate keeper need to be updated. However, in the SIP, an SIP application server which provides the new service is added, and the corresponding application is added. Then, the new service is usable.
Japanese Unexamined Patent Publication (JP-A) H11-341532A and an article entitled “SIP: Session Initiation Protocol” (RFC (Request for Comments) 3261, June 2002, pp. 8-34) disclose the earlier techniques described above.
In the known network described above, wireless terminals, such as PHS terminals, can connect to a private branch exchange via an access point included in a wireless LAN, but has a problem. Specifically, even when an SIP-compliant wireless terminal is covered by services of the private branch network, only limited services (e.g., a transfer service, three-way calling service, and call waiting service) defined by IETF (Internet Engineering Task Force) can be offered for communication between the wireless terminal and the SIP terminal.
That is, even when the wireless terminal and the SIP terminal are connected to the network, there is a problem in that a wide range of services (e.g., a call-back service, extension-call interruption service, third-party control service) are not available for communication between the wireless terminal and the SIP terminal.
Further, since the wireless terminal is connected to the private branch exchange via an access point, the wireless terminal can connect to the private branch exchange anytime and anywhere as long as an access point exists at a location to which the user of the terminal wireless moves. This makes it difficult to keep a track of the current location of the user.